1. Field of the Invention
The present invention relates to a method of supporting hand-off decision for guaranteeing continuous mobility of a dual-mode mobile terminal between a plurality of different mobile communication network systems, more particularly, to a method of supporting hand-off decision of a dual-mode mobile station in a mixed communication network where a synchronous and an asynchronous communication system coexist when the dual-mode mobile station is about to move to other areas being serviced by different network system.
2. Description of the Related Art
According to development of mobile communication technologies and mobile networks, various mobile communication network systems are being developed and works on standardization thereof are in progress.
The mobile network system having been developed from a mobile phone network is bisected into a synchronous system based on IS-95 led by US at present and the asynchronous GSM system developed by ETSI, which is a key leader. Especially, the worldwide market share of the asynchronous system has reached over 80 percent.
In present, IMT-2000, the 3rd generation (called ‘3G’ hereinafter) mobile communication system, is being standardized, and the system and radio frequency thereof are being designed to support global international roaming service. However, it is unlikely possible to derive mutually-agreed standard and system specification among related nations due to their own interests. Namely, standardization and development of IMT-2000 are in progress independently at two parties, one for W-CDMA system led by Japan and Europe, and the other for IS-2000 system led by US.
In Korea, the existing 2nd generation (called ‘2G’ hereinafter) mobile phone system, which is commercially in service, is synchronous one, and commercialization of CDMA 2000 system, which is the earliest system of IMT-2000, is being promoted.
Service providers, however, want to use asynchronous W-CDMA as 3G system on the grounds that the 3G system is likely to adopt the W-CDMA system, therefore, a synchronous and an asynchronous system will coexist in Korea when the 3G system is introduced commercially.
If the present 2G mobile communication providers are chosen to the 3G mobile communication provider too, there will be occurred a hand-off problem between an asynchronous and a synchronous system when supporting mobility between two different systems.
The asynchronous and the synchronous network system have different channel structure and service capability each other, therefore, a hand-off between two different systems should be conducted after checking service access capability, namely, terminal capability of a mobile station.
Most previous researches on hand-off is focused on sync acquisition which is indispensable in case of a hand-off from the asynchronous to the synchronous system, and user data and service capability are hardly considered in the previous researches.
It is very important to support a hand-off between an old and a new network system from the standpoints of initial investment cost and recycling of already-installed system resources if most of the 2G mobile communication providers are decided to the 3G mobile communication providers, too. The synchronous and the asynchronous system are operated in accordance with mutually different protocol structure and procedure. Accordingly, for supporting smooth hand-off between the two different systems, there should be proposed a new method of determining a hand-off without affecting the existing procedures.
In communication circumstance of Korea running synchronous 2G system, an adoption of IMT-2000 of asynchronous system would cause several problems against efficient service.
First of all, apart from the existing network resources, a new mobile communication resources are needed to be constructed to introduce an asynchronous system, which requires enormous initial investment cost and very long network establishing time.
Furthermore, a new solution is needed for effective use of both the existing 2G system and the new 3G one. The solution considered in general is to install and start the asynchronous 3G system in part from heavy-traffic service territories, and to expand 3G service territories gradually. By doing this, the existing 2G system may be used as a supplementary network out of service coverage of the 3G system until the 3G system covers entirely.
For this gradual expansion of the 3G system, a new method of supporting a hand-off between the two different systems, each of which uses different protocol and communication scheme, should be invented. However, most researches related on a hand-off are focused on sync acquisition which is indispensable in case of a hand-off from the asynchronous to the synchronous system, as aforementioned.
Furthermore, although a sync acquisition problem is solved, protocol mismatch caused from different service protocols adopted by the two different systems should be also resolved.